Parker says criteria introduced in the 1980s broadened the definition of depression to include minor, everyday conditions.

"Clinical depression in the old days was black melancholia," says Parker. "Now we've got blue becoming the new black."

Current system saves lives

But Professor Ian Hickie of the University of Sydney rejects the idea that current diagnosis of depression is over-inclusive.

"Against what criteria is it over-inclusive? What's the benchmark?" he says.

Hickie says the more people that picked up by the criteria the better, since people with lesser forms of depression are more likely to be at risk from premature death than the general population, and to develop major depression later on.

"The increased treatment rate is a godsend," says Hickie, a past chief executive of the national depression initiative, beyondblue.

He says just as treating less-severe forms of hypertension helps save lives, so does treating less-severe forms of depression.

"This is where cardiology was 30 years ago," he says.

He disagrees with Parker's estimate that the current criteria would cover around 90% of the population, citing instead his "best guess" as 50%.

But he says the argument is "completely sterile" because there is evidence that the current approach to diagnosing and treating depression has saved lives.

"What we see is that when treatments have gone up suicide has gone down," he says.

Hicke also argues that a broader diagnosis has reduced the stigma of being "depressed", forcing the abandonment of old demeaning labels of "stress" and "nervous breakdown" that stopped people from seeking help.

Still, he says, only half of those in the community who fit the criteria for major depression are receiving treatment and that more should be treated.

Parker supports greater awareness and less stigmatisation of depression but he says the downside of such inclusive diagnostic criteria is that some people are being treated when they don't need to be.

He is also concerned that the current diagnostic criteria are too "dumbed down" and make it difficult for clinicians to diagnose the cause of the depression and select the best treatment.

Parker thinks many people are being treated with drugs who should be treated with other more effective means, and vice versa.

And he wants to educate the public and practitioners about an alternative model that focuses on identifying the driver of a person's depression to determine the best treatment.

"It's a much more 'horses for courses' model," he says. "Sometimes it will be a drug, sometimes it will be psychotherapy, sometimes it will be CBT [cognitive behavioural therapy] or counselling and sometimes it will be common sense support."

But Hickie says Parker's model assumes that the causes of depression are known and can be used to deduce the best treatment.

There is no consensus on the causes of depression, says Hickie, which means clinicians can only use their judgement about what works to determine the treatments they provide.

Parker acknowledges his is a minority position but says support for it is increasing.